Categories of drug include stimulants, depressants, hallucinogens, dissociatives, opioids, inhalants and cannabinoids, and each comes with its own set of characteristics, effects and dangers.^1-3

While the pharmacological mechanisms for each class of drug are different, the activation of the reward system is similar across substances in producing feelings of pleasure or euphoria.^1-3

The ‘Gateway Theory’ suggests that some drugs act as a ‘gateway’ to other drugs.³ People may choose to use several drugs for many reasons including:

• Curiosity about the drug itself and its effects.
• To cope with the ‘comedown’ of one drug by using another e.g., using a benzodiazepine following heavy cocaine use - ‘uppers’ and ‘downers’.
• To ‘treat’ withdrawal symptoms of one drug with another.
• To enhance the feelings of one drug with the use of another e.g., ‘speedball’.
• Direct substitution e.g., a heroin user stops taking heroin but turns to alcohol instead.
• A drug dealer could introduce their client to other drugs due to the access they have.

Substance use disorders span a wide variety of problems arising from substance use, and cover 11 different criteria:^4,5

1. Taking the substance in larger amounts or for longer than intended.
2. Wanting to cut down or stop using the substance but not managing to.
3. Spending a lot of time getting, using, or recovering from use of the substance.
4. Cravings and urges to use the substance.
5. Not managing to do what is expected at work, home, or school because of substance use.
6. Continuing to use, even when it causes problems in relationships.
7. Giving up important social, occupational, or recreational activities because of substance use.
8. Using substances again and again, even when it puts the individual in danger.
9. Continuing to use, even when there is a physical or psychological problem that could have been caused or made worse by the substance(s).
10. Needing more of the substance to get the desired effect (tolerance).
11. Development of withdrawal symptoms, which can be relieved by taking more of the substance (or sometimes using another substance).

Multi-drug addiction is managed through:^6,7

• Identification of the substance used, the amount used and mode of use.
• Stabilisation of substance use (if appropriate).
• Substitute prescribing (e.g., methadone) or detox (if appropriate).
• Treating any physical health problems.
• Mental health assessment and treatment.
• Onward referral which may include drug treatment services, psychology, cognitive behavioural. therapy (CBT), housing, etc.
• Regular review and follow-up.
• Possible placement in a rehab facility.

The known risks associated with multi-drug addictions include:^8-10

• Increased risk of untoward symptoms of withdrawal such as seizure and hallucinations.
• Increased physical ill health.
• Development of cancers.
• Development of chronic conditions.
• Reduction in maintaining good health e.g., nutrition, taking medication, managing conditions such as diabetes, etc.
• Risk of accidents.
• Risk of criminal behaviour.
• Accidental overdose.
• Mental health issues.

Substance misuse can have a wide range of short and long-term, direct and indirect effects on health. These effects often depend on the specific drug or drugs used, how they are taken, how much is taken, the person's health, and other factors.

Short-term effects can range from changes in appetite, wakefulness, heart rate, blood pressure, and/or mood to heart attack, stroke, psychosis, overdose, and even death.